This invention relates generally to wire guides used to position a catheter or other medical tool at a precise location within a patient.
Wire guides are used routinely in various medical procedures. In order to negotiate a tortuous path or avoid obstacles during insertion, wire guides normally include a floppy tip that is often biased in a certain direction. However, it is desirable that the remaining portion of the wire guide be somewhat elastic and resistant to kinking but still able to transmit a torque so that the doctor can change the direction of the biased tip to make a turn or avoid an obstacle while advancing the wire guide into position. It has been found that using a shape memory material, such as a nickel titanium (NiTi) alloy, in the body of the wire guide has significant advantages over conventional steel wire guides in that NiTi's "super elastic" properties can allow doctors to reach much more remote locations within the body. In other words, certain nickel titanium alloys are simply more kink resistant than conventional stainless steel. Unfortunately, however, NiTi alloys are not easily bonded to other materials, making it troublesome to use in manufacturing the distal tip of the wire guide.
In order to obtain a desired flexibility at the tip, wire guides are often tapered at their distal end, and often include a coil spring extending over the tapered portion and a smoothly rounded tip attached at the distal end of the mandrel. The smoothly rounded tip must normally be welded to the mandrel. However, because NiTi alloys are generally not easily bonded to other metals, attaching the rounded tip to a NiTi mandrel is a difficult procedure.
What is needed is a mandrel for wire guides which is substantially kink resistant over the majority of its length but which also retains the manufacturing advantages and reliability of stainless steel at its distal end.